package com.nercel.dsj.gksales.util;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * @author sunlin
 * @date 2018-12-11
 */
public class Md5Util {
	private static char hexDigits[] = {'0', '1', '2', '3', '4', '5', '6', '7',
			'8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
	private static MessageDigest messagedigest = null;

	static {
		try {
			messagedigest = MessageDigest.getInstance("MD5");
		} catch (NoSuchAlgorithmException e) {
			// logger.error("MD5FileUtil messagedigest init fail.", e);
		}
	}

	/**
	 * 获取文件的MD5值
	 */
	public static String getFileMD5String(File file) throws IOException {
		return getFileMD5String(file, 0, -1);
	}

	/**
	 * 获取文件的MD5值
	 */
	public static String getFileMD5String(File file, long start, long length)
			throws IOException {
		FileInputStream fis = new FileInputStream(file);
		FileChannel ch = fis.getChannel();

		long remain = file.length() - start;

		if (length < 0 || length > remain) {
			length = remain;
		}

		MappedByteBuffer byteBuffer = ch.map(FileChannel.MapMode.READ_ONLY,
				start, length);

		messagedigest.update(byteBuffer);
		return bufferToHex(messagedigest.digest());
	}

	/**
	 * 获取字符串的MD5加密的结果
	 */
	public static String getMD5String(String s) {
		return getMD5String(s.getBytes());
	}

	public static String getMD5String(byte[] bytes) {
		messagedigest.update(bytes);
		return bufferToHex(messagedigest.digest());
	}

	private static String bufferToHex(byte[] bytes) {
		return bufferToHex(bytes, 0, bytes.length);
	}

	private static String bufferToHex(byte bytes[], int m, int n) {
		StringBuffer stringbuffer = new StringBuffer(2 * n);
		int k = m + n;
		for (int l = m; l < k; l++) {
			appendHexPair(bytes[l], stringbuffer);
		}
		return stringbuffer.toString();
	}

	private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
		char c0 = hexDigits[(bt & 0xf0) >> 4];
		char c1 = hexDigits[bt & 0xf];
		stringbuffer.append(c0);
		stringbuffer.append(c1);
	}

}
